In some industrial, construction, earth-moving, mining, agricultural, and other applications of drive trains, the engine load on an internal combustion engine may fluctuate. For example, the engine load on an internal combustion engine in a combine may increase as the vegetation density or yield increases in certain zones in a field. Although torque can be increased by turbo-charging or super-charging a naturally aspirated, internal combustion engine, there is typically a material lag associated with the torque increase. The material lag tends to make turbo-charging or super-charging ineffective in dealing with sudden or unexpected increases in engine load. Accordingly, there is a need to provide rapid or responsive boosting of torque of a drive train.